SIGNAL TRANSDUCTION BY HETEROTRIMERIC G PROTEINS
Our research focuses on signal transduction by G proteins. We use biochemical, genetic, molecular and cellular approaches to uncover fundamental mechanisms that govern G protein signaling and function. 1. G protein regulation of tyrosine kinases: We have been examining the regulation of nonreceptor tyrosine kinases by G proteins. We used a molecular genetic approach to identify the specific nonreceptor tyrosine kinases involved in specific G protein signaling pathways in vertebrate cells. Then, using a biochemical approach, we demonstrated that some G proteins could directly stimulate the activity of purified nonreceptor tyrosine kinases. These studies not only show that certain tyrosine kinases are new direct effectors of G proteins, but also demonstrate that a single Ga subunit can transmit cellular signals to multiple targets. We are undertaking biochemical, structural, and transgenic mouse studies on G protein regulation of tyrosine kinases. These lines of research will broaden our understanding of the activation mechanism of tyrosine kinases, the physiological function of G proteins, and the cross-talk of the two most widely used cellular signaling mechanisms. 2. G protein network: interplay of heterotrimeric and monomeric G proteins: Monomeric G proteins are key signaling molecules. Through their ability to control and disseminate information flow, they not only regulate many aspects of cell growth and differentiation, but also mediate such diverse physiological processes as vesicular trafficking, nuclear transport, tumorigenesis, apoptosis and actin cytoskeletal arrangement. The Ras superfamily of monomeric G proteins is comprised of over 60 distinct mammalian members that can be divided into several subfamilies (Ras, Rho, Rab, Arf, Ran and Gem). The functional interplay between heterotrimeric and monomeric G proteins in signal transduction has recently emerged as an exciting field of intensive investigation. Monomeric G proteins have been implicated in mediating a variety of heterotrimeric G protein signaling pathways. However, it is not clear how heterotrimeric G proteins are biochemically connected to monomeric G proteins. We are investigating possible mechanisms by which heterotrimeric G proteins and G protein-coupled receptors biochemically regulate Rho-family G proteins. 3. G protein regulation of cancer metastasis: The main cause of treatment failure for cancer patients is metastasis - the formation of secondary tumors in organs a distance from the original cancer. Secondary tumors are seeded by cells released from the original tumor and ferried about the body in lymphatic and blood circulation. It is not clear why some organs have large numbers of secondary tumors, while other organs have relatively few. Recently it has been shown that interactions between chemokines and their G protein-coupled receptors play a critical role in human breast cancer metastasis. Breast cancer metastssis in animals could be blocked by antibodies that neutralize certain chemokine receptors. We are in the process dissecting this signaling pathway, in hopes of finding targets for drug development. 4. G protein regulation of aging: The life span of animals is genetically controlled. Two kinds of genes affect aging rates. The rate of cellular aging can be regulated by genes that directly affect intracellular mechanisms for protection, turnover, and repair of macromolecules and cell membranes. Examples are genes for enzymes that eliminate free radicals, such as superoxide dismutase and catalase. A second class includes genes that act systemically to control the aging of the organism as a whole. Recently, a genetic screen for gene mutations that extend life-span in Drosophila has isolated a mutant methuselah (mth) that displays increased average life-span and enhanced resistance to various forms of stress. The mth gene encodes a G protein-coupled receptor. It is known that G protein-coupled receptors are involved in controlling metabolism, food intake, body weight, energy expenditure, the sleep-wake cycle, and many other physiological functions. Our aim is to understand the biochemical mechanisms how certain G protein-coupled receptors mold the aging process. 5. Kinetic and spatiotemporal studies of G protein signaling processes in single living cells: We are using bioluminescence resonance energy transfer, confocal and fluorescence microscopes to study the biochemistry of a cell. We are examining the interactions of G proteins with other signaling molecules in single living cells to ascertain the kinetic and spatiotemporal aspects of G protein signaling. 6. Transgenic studies of the physiological functions of the new G protein signaling pathways: We have identified several novel G protein effectors. However, the relative contribution of these new effectors and the previously identified effectors to G protein physiological functions has not been studied. We are generating transgenic mice overexpressing G proteins, and we hope to cross these transgenic mice with effector knockout mice to dissect the roles of each G protein effector pathway. We also hope to use tissue-specific conditional gene disruptions and point mutation knockin for these animal physiological studies. 7. Structural basis of G protein signaling: To provide a structural basis for the activation mechanism of tyrosine kinases (and other effectors) by G proteins, we collaborate with some structural biology laboratories to provide new insights into the interactions of G proteins with tyrosine kinases (and other effectors), which would be extremely useful in guiding the design of specific inhibitors for specific G protein signaling pathways for use in animal physiological studies. e-mail: firstname.lastname@example.org Please click here for further information.